1. Field of the Invention
The present invention relates to a process for producing trisilylamine from monochlorosilane and ammonia in the liquid phase. The present invention further relates to a plant wherein such a process can be carried out.
2. Discussion of the Background
Trisilylamine (TSA), N(SiH3)3, is an extremely mobile, colourless, self-ignitable and readily hydrolyzable liquid having a melting point of −105.6° C. and a boiling point of +52° C. Nitrogen-containing silicon compounds such as trisilylamine are important substances in the semiconductor industry.
It has long been known to use TSA to produce silicon nitride layers (U.S. Pat. No. 4,200,666, JP 1986-96741). TSA more particularly finds application in chip manufacture as a layer precursor for silicon nitride or silicon oxynitride layers. EP 1 547 138 for example discloses a very specific process for using TSA. Owing to its use in chip manufacture, it is important to be able to produce trisilylamine in the required, generally ultrapure quality in a safe, reliable and consistent manner.
Trisilylamine is synthesizable from monochlorosilane and ammonia as per the following equation:3H3SiCl+4NH3→N(SiH3)3+3NH4Cl  (1)
Ammonium chloride is by-produced. The reaction of monochlorosilane and ammonia is a spontaneous, exothermic reaction.
Alfred Stock and Karl Somieski in Ber. Dtsch. Chem. Ges. 54, 740 ff., 1921, report the immediate reaction of monochlorosilane gas and ammonia gas at room temperature in accordance with equation (1). The reaction proceeds with excess monochlorosilane to produce quantitative trisilylamine. By-produced ammonium chloride separates out.
WO 2010/141551 describes the reaction of monochlorosilane with ammonia in the gas phase. WO 2011/049811 teaches producing silylamines as closely as possible to the site of use in order to minimize the delivery distance and hence the delivery time. According to WO 2011/049811, TSA-containing silylamines are obtainable from monochlorosilane and ammonia both in the gas phase and in the liquid phase.
US 2011/0178322 describes a process for producing trisilylamine by thermal decomposition of perhydropolysilazanes in an oxygen-free or low-oxygen atmosphere.
Richard L. Wells and Riley Schaeffer in J. Am. Chem. Soc. 88, 37 ff., 1966, already describe reacting monochlorosilane with ammonia by warming a mixture of the two compounds from −196° C. to room temperature. In addition to trisilylamine formation as per equation (1), a sequence of descendent reactions is observed:3(SiH3)3N+nNH3→3SiH4+nNH3+(SiH3NSiH2)3  (2)(SiH3NSiH2)3+xNH3→ySiH4+zNH3+“polymeric material”  (3)
Thus, trisilylamine can react further in the presence of ammonia to form monosilane (SiH4) and N,N′,N″-trisilylcyclotrisilazane (SiH3NSiH2)3 and also “polymeric material”. Descendent reactions (2) and (3) have a disadvantageous effect on the yield of trisilylamine.